var jsonStr = JSON.stringify(list); 
var param= {}; 
param.jsonStr=jsonStr; 

List<T> list = new ArrayList<T>(); 
JSONArray jsonArray = JSONArray.fromObject(str);//把String转换为json 
list = JSONArray.toList(jsonArray,t);//这里的t是Class<T> 

JSONArray json = JSONArray.fromObject(object); 
String str = json.toString();//把json转换为String 

/** 
  * @param answers 
  * @param question_ids 
  * @param types 
  * @return 
  */ 
 private List<Answer> toAnswerList(String[] studenAnswers, int[] question_ids, 
   int[] types,int[] scores) { 
  List<Answer> answerList = new ArrayList<Answer>(); 
   
  if(studenAnswers!=null && question_ids!= null && types!= null&& scores!= null){ 
   for (int i = 0; i < studenAnswers.length; i++) { 
     
    Answer answer = new Answer(); 
    String studenAnswer = studenAnswers[i]; 
    int type = types[i]; 
    int question_id = question_ids[i]; 
    int score = scores[i]; 
   
     
    answer.setQuestion_id(question_id); 
    answer.setScore(score); 
    answer.setStudenAnswer(studenAnswer); 
    answer.setType(type); 
     
    answerList.add(answer); 
   } 
  } 
  return answerList; 
 } 
 
 /** 
  * 将一个json字串转为list 
  * @param props 
  * @return 
  */ 
 public static List<Answer> converAnswerFormString(String answer){ 
  if (answer == null || answer.equals("")) 
   return new ArrayList(); 
 
  JSONArray jsonArray = JSONArray.fromObject(answer); 
  List<Answer> list = (List) JSONArray.toCollection(jsonArray, 
    Answer.class); 
   
  return list; 
 } 

 public String getAnswerString(String[] studenAnswers, int[] question_ids, 
   int[] types,int[] scores) { 
  List list = toAnswerList(studenAnswers, question_ids, 
     types, scores); 
  JSONArray jsonarray = JSONArray.fromObject(list); 
 
  return jsonarray.toString(); 
 }